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GPS Microstrip Antenna Array on a Resistivity Tapered Ground Plane for Multipath Mitigation
April 2000
Basrur Rama Rao, The MITRE Corporation
Jonathan H. Williams The MITRE Corporation
Eddie N. Rosario, The MITRE Corporation
Robert J. Davis, The MITRE Corporation
ABSTRACT
GPS Carrier Multipath is a major source of error in Differential GPS
that cannot be removed through signal processing in the receiver; it
occurs from a variety of structural and ground reflections and is common
to both land based and airborne GPS systems. In this paper we describe
a new type of low profile, lightweight two-element microstrip antenna
array used in combination with a resistivity tapered ground plane for
reducing multipath in GPS systems. The concentric two-element array
consists of an outer annular ring microstrip antenna enclosing a centrally
located circular microstrip antenna. This antenna array is used as a
polarization filter for adaptive cancellation of the cross polarized
multipath signals; the function of the resistivity tapered ground plane
is to reduce the back radiation lobes of the antenna by attenuating
the signals that are either diffracted or reflected from the edges of
the ground plane. A Proof of Concept (POC) version of this antenna that
operates in the GPS L1 band has been built and tested to demonstrate
feasibility of this concept. A dual band version that operates at both
the GPS L1 and L2 frequency bands can be built by using stacked microstrip
patch antenna elements. This new antenna offers significant advantages
in terms of size, weight and cost over other multipath mitigation antennas
such as the choke ring ground plane antenna or the three element vertical
linear array. It is especially attractive for installation on airborne
platforms because of its low profile, which is not possible with the
much taller multi-element array. The microstrip antenna elements can
be manufactured using printed circuit technology to reduce cost; the
resistivity tapered ground plane can be made from different types resistive
material that are currently available such as textiles, composites,
paints or thin films sputtered on thin plastic sheets. Since it does
not need stamped or machined metallic parts like the choke ring ground
plane, it is easier and less expensive to manufacture and also lighter
in weight.
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